Oxidation catalyst



United States Patent 3,211,671 OXIDATION CATALYST Robert B. Egbert,Stamford, Conn, assignor to Chemical Process Corporation, Hamilton,onn., a corporation of Massachusetts No Drawing. Continuation ofapplication Ser. No. 820,861, June 17, 1959. This application July 16,1962, Ser. No. 210,202

Claims. (Cl. 252-437) This application is a continuation of Serial No.820,861, filed June 17, 1959, entitled, Oxidation Catalyst, nowabandoned.

The present invention is directed to the production of catalysts of thevanadium-molybdenum type, more particularly to catalysts especiallyadapted for high efficiency of conversion of benzene to maleicanhydride.

It has been known that a catalyst consisting essentially of a mixture ofthe oxides of vanadium and molybdenum, and supported on a ceramicallybonded fused alumina support having a low surface area and a highporosity, may be used in the oxidation of benzene to maleic anhydride.It has now been found that a catalyst of this composition is not veryactive or 'efficient as it does not bring about nearly completeconversion of the benzene at temperatures of about 760 F. or less. Whilethe efficiency is increased at higher temperatures, such hightemperatures cause rapid deterioration of the catalyst, so that the lifethereof becomes too short for economical operation.

To overcome these deficiencies, it has been proposed to add a smallproportion of phosphorus pentoxide in the form of phosphoric acid, inthe absence of alkali and alkali earth metals to a catalyst of theoxides of vanadium and molybdenum. The catalyst gave poor yields ofmaleic anhydride and the conversion of benzene was low. Hightemperatures were necessary, greatly reducing the life of the catalyst.

The present invention is intended and adapted to overcome thedisadvantages and difficulties encountered in the prior art, it beingamong the objects thereof to provide a catalyst of the above describedcharacter which is capable of bringing about substantially completeconversion of benzene at relatively low temperatures and below about 760F.

It is also among the objects of the invention to provide such a catalystwhich exhibits a high efliciency of reaction to produce maleic anhydridefrom benzene with excellent yields.

The basis of the present invention is the discovery that the addition ofcertain promoters, namely oxides of nickel, cobalt or iron, combinedwith the addition of phos phoric acid plus sufficient sodium, lithium,calcium or strontium to equal or exceed the amount of sodium, lithium,calcium or strontium required to produce the tribasic salt of phosphoricacid, results in a considerable improvement in yield. The results aresurprising in that neither the first group, namely nickel, cobalt oriron, nor the second group of sodium, lithium, barium or strontium, norphosphoric acid alone, nor any combination of two of the'three groupsalone, produce the desired results (namely, increased selectivity andyield). The results are further surprising in that the other alkali oralkaline earth metals such as potassium, rubidium, cesium, magnesium orbarium, cannot be substituted for the four mentioned above. They haveeither no effect or are actually harmful as in the case with rubidiumand cesium. It is also surprising-that the phosphoric acid must notexceed that corresponding to the tribasic salt of the sodium, lithium,calcium or strontium. Of the three elements, nickel, iron and cobalt,the cobalt and the Patented Oct. 12, 1965 ice iron are the moreeffective in increasing both the yield and the activity. When thepreferred catalyst is used the addition of cobalt or iron in place ofnickel increases the yield by 15%.

It is also possible, and even desirable, to. use mixtures of two or moreof the four alkali and alkaline earth metal oxides with the addition ofcobalt or iron oxide and phos phorous pentoxide. Large amounts of thesecombined promoters are unnecessary; less than 10% of the totalvanadium-molybdenum oxides suflice to produce an active catalyst. Acatalyst composition which has been found quite effective has thefollowing active constituents in parts by weight:

In practicing the invention, the following procedure was used inpreparing the various catalysts:

The desired amount of molybdenum oxide was introduced by dissolvingammonium molybdate in concentrated hydrochloric acid. Then the desiredamount of ammonium vanadate was dissolved in the solution. The cobaltwas introduced by dissolving'cobalt nitrate in the solution. The alkaliand/or alkaline earth metal prometer and phosphoric compounds may beintroduced in any suitable form, for instance, sodium in the form ofsodium chloride, the phosphorus in the form of phosphoric acid orphosphorus pentoxide, or both may be introduced as trisodium phosphate.

The resulting solution of the mixture of compounds was mixed withgranules of ceramically bonded fused porous alumina, and subjected toevaporation, resulting in the deposition of the catalytic materials onthe surface and in the pores of the support or carrier. The catalystcarrier was then calcined in the presence of air in a kiln held at aconstant temperature of about 750 F.

For practical operating reasons it is necessary to employ a supportmaterial to retain the catalyst in the reactor as the active catalystitself prepared in the manner described above in the absence of -acarrier would be a very fine crystalline powder which would be carriedaway by the flowing air-benzene mixture. This carrier material is itselfnot critical as long as it is insoluble in the concentrated acid used tomake thecatalyst. It needs to be sufliciently porous so that thereaction gases can diffuse in and out of the support. An ideal supportis made by ceramically bonding alumina, quartz, or silicon carbidegrains in such a manner that large pores are left-having diameters of50-150 microns, or larger.

The following are specific examples of catalysts made in accordance withthe present invention by the above procedure:

EXAMPLE 1 A catalyst Was made up having the following composition, thepercentages of the constituents being by weight:

Percent Vanadium (as V 0 8.7 Molybdenum (M00 5.4

Conversion:

Mols benzene oxidized Mols benzene fed Yield:

Mols benzene converted to maleic anhydride Mols benzene fed Efiiciency=Mols benzene converted to maleic anhydride Mols benzene oxidized EXAMPLE2 A catalyst similar to that of Example 1 was made up with cobalt addedas a promoter. It had the following composition:

Percent Vanadium (as V 8.3 Molybdenum (as M00 3.9 Cobalt (as C00 0.32

Oxidation of the benzene was conducted by the procedure described inExample 1, at 700 F. The conversion was 21.5% and the yield was 12%. At760 F. the conversion increased to 34.5% and the yield to 22.4%

Both of the above catalysts are too inactive for commercial use. It isalso seen that the addition of cobalt produced no appreciable effect.

EXAMPLE 3 A catalyst similar to that of Example 1 was made up exceptthat lithium oxide was incorporated into the catalyst. It had thefollowing composition:

Percent Vanadium (as V 0 8.7 Molybdenum (as M00 5.4 Lithium (as Li O)0.17

When tested under conditions similar to Example 1, the conversion at 700F. was 68% and the yield was 47%. At 760 F. the conversion was 90% andthe yield 55%.

EXAMPLE 4 A catalyst similar to that of Example 3 was made up exceptsodium oxide was used as a promoter. It had the following composition:

Percent Vanadium (as V 0 8.7 Molybdenum (as M00 5.4 Soduim (as Na O) 0.5

When tested under conditions identical to Example 1, the followingresults Were obtained. At 700 F. the conversion was 60.5% and the yield54.8%. At 760 F. the conversion was 87.8% and the yield 69%.

EXAMPLE 5 A catalyst was made up using calcium oxide as a promoter. Ithad the following composition:

Percent Vanadium (as V 0 8.7 Molybdenum (as M00 5.4 Calcium (as CaO)0.53

At 700 F. the conversion was 71% and the yield was 47.8%. At 740 F. theconversion was 93.1% and the yield 65.6%.

4 EXAMPLE 6 A catalyst was made up using stronium chloride as apromoter, having the following composition:

Percent Vanadium (as V 0 8.7 Molybdenum (as M00 5.4 Strontium (as SrO)0.9

At 700 F. the conversion was 65% and the yield was 42%. At 740 theconversion was 86% and the yield was 55.5%.

Other promoters were tried, and the results are tabulated in thefollowing tables Tables I-A and IB.

Table I-A.Catalysts containing 8.7% V 0 and 5.4%

Table IB.Catalysts conltaining 8.3% V 0 3.9% M00 and 0.32% c0 0Conversion, Yield Concentrapercent percent Promoter tration wt.

percent (as oxide) 700 F. 760 F. 700 F. 760 F.

Potassium 0. 27. 5 37 17 22 Rubidium 0. 78 11. 7 27 5. 6 19 Cesium 1.1310. 3 27 7. 2 18 Magnesium. 0. 39 27 55 17 36 Barium 1.17 17 25 34 35 Ascan be seen from the above examples, the addition of lithium sodium,calcium or strontium oxides is beneficial to the activity and yield ofthe catalyst, while the other alkali and alkaline earth metal oxideshave little effect or are even detrimental. Also the addition of cobaltto the unpromoted catalyst or to catalysts made using the promoterslisted in Table I above has little or in some cases a deleteriouseffect. Likewise, the addition of cobalt had little or no effect oncatalysts promoted with lithium, sodium, calcium and strontium. Theeffect of cobalt on these catalysts is tabulated below in Table II.

Table Il.--Efiect of cobalt on catalyst activity and yield [Catalystscontaining 8.7% V10 5 and 5.4% M003] Promoters Temp, Conversion, Yield,mol

F. percent percent 0.5% sodium oxide 650 28. 5 22. 4 0.5% sodium oxide;0.32% cobalt oxide 650 30. 0 21. 3 0.5% sodium oxide 760 87. 8 69. 00.5% sodium oxide; 0.32% cobalt oxide 760 94. 1 68. 0 0.17% lithiumoxide 680 60. 0 41. 6 0.17% lithium oxide; 0.32%

cobalt oxide 680 59. 5 41. 6 0.53% calcium oxide 735 93.1 65.6 0.53%calcium oxide; 0.32%

cobalt oxide 735 92. 9 62.8 0.9% strontium oxide 740 86.1 55. 5 0.9%strontium oxide;

cobalt oxide 735 92. 9 62. 8

Likewise, the addition of phosphorous pentoxide has no beneficial effectand is indeed in some cases deleterious. Table III below tabulatesresults obtained when phosphorous pentoxide was added to variouscatalysts.

Table IIl.-Efiect of phosphorous pentoxide n the activity of thecatalyst prepared as in Example 1 yield greatly with very lowefliciencies.

[Catalysts containing 8.3% V 0 and 3.9% M003] ing them both to the basicmolybdenum vanadium oxide catalyst in the absence of these promotersdecreases the Referring to Table III it can be seen that conversion ofthe unpromoted catalyst is unchanged but the yield was decreased by afactor of between three and four.

To compare the relative effectiveness of iron, nickel in Table V.

and cobalt as promoters in the presence of phosphoric acid andsufficient sodium oxide to form the tribasic salt of phosphoric acid, along term test was run. Identical quantities of vanadium, molybdenum,phosphorous and sodium were used. The comparison was made in amulti-tube react-or with identical temperatures, flowrates and benzeneconcentrations to each one. The benzene concentration was held at 1.2percent. The space velocity was 2400 standard cu. ft. of gas-benzenemixture per cu. ft. reactor volume.

The results are summarized Table V.C0mparis0n of nickel, iron and cobaltpromoted catalyst Elapsed Tillie-.. Initial 372 hrs. 500 hrs. 644 hrs.690 hrs. 982 hrs. 1,024 hrs.

Temperature 700 F. 715 F. 715 F. 715 F. 728 F. 744 F. 754 F.

Conver- Yield,

sion mol t Oonv. Yield Conv. Yield Conv. Yield Conv. Yield Conv. YieldConv. Yield percen Nickel promoted catalyst 57. 2 39 86.3 53. 0 78.8 57.5 73. 3 53. 2 83. 8 63 92. 5 67 94. 2 65. 7 Cobalt promoted catalyst60.3 49 91. 1 64. 8 84. 3 65. 6 79. 5 61. 5 89. 5 69 94. 2 70. 5 96.373.0 Iron promoted catalyst 91 72. 3 89. 4 63. 8 83. 4 64. 3 79. 7 61. 588. 3 72. 3 92. 8 73. 4 96. 8 74. 7

Table IV.-Catalyst containing 8.3% to 8.7% V 0 and 3.9% to 5.4% M00Promoters Temp, Conversion, Yield, mol

F. percent percent 0.5% sodium oxide 8 0.11% NazO; 0.088% P20 700 68 56.0

0.32% C00 760 96. 7 80. 6 0.36% N820; 0 8% P20 0.32% C00 700 95. 3 75. 80.16% lithium oxide 700 77. 8 54. 2 0.069% LizO; 0.14% P 0 700 80. 4 63.7

L110; 0.32% C00 710 99. 0 71. 3 0.53% 0210; 0.11% N e20; 0.088%

The beneficial result of adding cobalt oxide and phosphorous pentoxideto the alkali and alkaline earth promoters is indeed surprising in lightof the fact that add- The proportions of the various promoters can varyover fairly wide limits. The ratio of molybdenum oxide to vanadiumpentoxide can vary over a fairly wide range, from 0.25 to 1.5. Thepreferred range is 0.4 to Most of the catalysts described in theexamples above had a ratio MoO /V 0 :0.67.

The amount of alkali metal or alkaline earth oxide bination of eachother. tween 1.0 and 6.0%.

can vary from 0.5% to 10% of the total active oxides present. They canbe present separately or in any com The preferred amounts lie be- Theamount of cobalt oxide can also be varied over the range of 0.5 .to 10%of the total active materials with a preferred range of 1.5 to 5%.

The proportion of active material on the support depends c-onsiderablyon what support is used. With the fused aluminum oxide supports studiedthe minimum amount of active materials should be 5% of the weight of thesupport with preferred range between 8 and 15%.

The proportions of phosphorous pentoxide are critical.

The amount of phosphorous pentoxide must always be equal to or less thanthat required to form the tribasic salt with the alkali or alkalineearth metal oxide.

In the above examples the alkali promoters have been This was merelydone for The true composition of the catalyst is Most of the catalystsabove were prepared from solutions in hydrochloric acid. However, thisis not critical nor necessary to produce a good catalyst. Oxalic acidgave identical catalyst to that prepared from hydrochloric acid. Otheracids could also be used. The advantage of hydrochloric acid is the factthat the various metal salts are quite soluble in it, permitting thethorough impregnation of the support, and the excess acid is easilyremoved by evaporation of the solution.

I claim:

1. A catalyst for the oxidation of benzene to maleic anhydride whichconsists essentially of a mixture of oxides of molybdenum and vanadiumand containing as promoter (1) the oxide of an alkaline metal taken fromthe group consisting of sodium, lithium, calcium and strontium in anamount of 1.0% to of the total oxides of molybdenum and vanadium,

(2) an amount of phosphorus pentoxide not more than that correspondingto the tribasic salt of said alkaline metal and not less than one-tenthof said amount,

(3) and the oxide of a heavy metal taken from the class consisting ofcobalt and iron in an amount from one-half to twice the amount of saidalkaline metal oxides.

2. An oxidation catalyst according to claim 1 characterized in that amixture of at least two of said alkaline metal oxides is present.

3. An oxidation catalyst according to claim 1 characterized in that theamount of phosphorus pentoxide is about one-half of that required forsaid tribasic salt.

4. An oxidation catalyst according to claim 1 characterized in that theoxides present are those of molvbdenum, vanadium, cobalt, sodium andphosphorus.

5. An oxidation catalyst for the oxidation of benzene to maleicanhydride consisting essentially of the following active constituents inthe approximate proportions by weight:

Molybdenum oxide 8.7

Vanadium oxide 5.4

Cobalt oxide .34 Sodium oxide .26 Phosphorus pentoxide .15

References Cited by the Examiner UNITED STATES PATENTS 2,691,037 10/54Bellringer et al 252435 X 2,967,185 1/61 Becker et al 252437 X 3,086,0264/63 Wiebusch 252437 X MAURICE A. BRINDISI, Primary Examiner.

1. A CATALYST FOR THE OXIDATION OF BENZENE TO MALEIC ANHYDRIDE WHICHCONSISTS ESSENTIALLY OF A MIXTURE OF OXIDES OF MOLYBDENUM AND VANADIUMAND CONTAINING AS PROMOTER(1) THE OXIDE OF AN ALKALINE METAL TAKEN FROMTHE GROUP CONSISTING OF SODIUM, LITHIUM, ALCIUM AND STRONTIUM IN ANAMOUNT OF 1.0% TO 5% OF THE TOTAL OXIDES OF MOLYBDENUM AND VANADIUM, (2)AN AMOUNT OF PHOSPHORUS PENTOXIDE NOT MORE THAN THAT CORRESPONDING THETHE TRIBASIC SALT OF SAID ALKALINE METAL AND NOT LESS THAN ONE-TNETH OFSAID AMOUNT, (3) AND THE OXIDE OF A HEAVY METAL TAKEN FROM THE CLASSCONSISTING OF COBALT AND IRON IN AN AMOUNT FROM ONE-HALF TO TWICE THEAMOUTN OF SAID ALKALINE METAL OXIDES.